The present invention is directed generally to an improved inductive displacement sensor for use in a hydraulic accumulator, and more particularly, to an inductive displacement sensor arranged and constructed to reduce the volume of high-pressure gas in the hydraulic accumulator.
DE 198 52 628 A1 discloses a hydraulic accumulator, albeit without a built-in displacement sensor, which can be used for storing and supplying pressurized (hydraulic) fluid in a motor vehicle. The accumulator has a cylindrical housing divided by a bottom plate and a bellows into two separate pressure chambers. The bottom pressure chamber can be connected via a nozzle to the hydraulic system of the vehicle; the upper pressure chamber is filled with a suitable gas, such as nitrogen. When the fluid pressure becomes sufficiently high during filling of the hydraulic accumulator with hydraulic fluid, the bellows together with its charge of high-pressure gas becomes compressed, thus maintaining the desired hydraulic pressure.
Pressure sensors installed at appropriate positions in the hydraulic system monitor the hydraulic pressure. For various reasons, however, it is additionally desirable to monitor the position of the bottom plate of the hydraulic accumulator by displacement measurement. With this type of monitoring, it is possible to detect undesirable gas bubbles in the hydraulic system. The bubbles become compressed when the pressure of the hydraulic fluid is raised and inhibit the initial movement of the bottom plate of the hydraulic accumulator.
In another conventional design, the necessary filling charge of high-pressure gas in a hydraulic accumulator of the type described in DE 198 52 628 A1 can be reduced by using filler elements of incompressible material in the accumulator. This has the advantage that harmful temperature influences on the accumulator pressure are diminished by virtue of the smaller charge of high-pressure gas. Furthermore, the steepness of the pressure displacement characteristic of the hydraulic accumulator can also be increased.
DE 196 24 801 A1, which is incorporated herein by reference, discloses an inductive displacement sensor suitable for measuring the displacement of the bottom plate of a hydraulic accumulator. The displacement sensor has a coil into which an iron core can be inserted to an extent that depends on displacement. The coil is wound on a coil former. The coil former can have a plurality of chambers in which coil windings or winding segments with different numbers of turns or winding heights are disposed to achieve a uniform sensor characteristic. If a winding segment with a small number of turns or low winding height is provided, the annular space between the surface of the coil and the periphery of the coil former remains unoccupied. As a result, the volume filled by the high-pressure gas or the filling charge of the hydraulic accumulator becomes larger, thus diminishing the aforestated advantages of a small filling charge.
It is desired to improve the construction of an inductive displacement sensor for use in a hydraulic accumulator to achieve a desired additional reduction of the gas volume or filling charge of the hydraulic accumulator.
Generally speaking, in accordance with the present invention, an improved inductive displacement sensor for use in a hydraulic accumulator is provided. The displacement sensor includes a coil former containing windings of electrically conductive wire disposed in at least one chamber of the coil former. In addition to the electrical windings, further windings without electrical connections are wound about (i.e., over and/or under) the electrical windings to fill unoccupied space between the electrical windings and the coil former. Because the additional volume occupied by the further windings is permeable to pressure, the arrangement according to the present invention achieves a desired additional reduction of the volume of high-pressure gas in the hydraulic accumulator.
The further windings can be formed from plastic thread or like material suitable for the high pressures of up to 300 bar that can exist in hydraulic accumulators.
Accordingly, it is an object of the present invention to provide an improved inductive displacement sensor for achieving a desired additional reduction of the gas volume or filling charge in a hydraulic accumulator.
It is another object of the present invention to provide an improved inductive displacement sensor that can be easily and efficiently implemented in a hydraulic accumulator.
It is a further object of the present invention to provide an improved inductive displacement sensor that minimizes instrumental complexity and is cost-effective.
Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification.
The present invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.